Add "same as source" option for output extension

[x9sim9]

So the issue is that I am adding to the queue a list of files, some being mkv and some being mp4 file extension.

What happens is that if I set the file extension in profile to MP4 then any mkv file with a subtitle fails to encode with "not supported" message.

If i set the file extension to MKV then any mp4 file with a subtitle fails to encode with "not supported"

So instead of choosing the file extension, can we have an option to match source?